A pneumatic tire which can effectively run flat under load after losing its inflation pressure, for a satisfactory distance at relatively low speeds, has long been sought after. When a conventional pneumatic tire is run in its flat condition, a rapid heat build-up occurs from both internal friction and, normally, internal surface-to-surface contact, resulting in a destruction of part of the tire generally through a chemical breakdown of its components and consequent failure. Lubrication of the tire's inner surface has been the primary proposed solution to retard the heat build-up. Indeed, the technical art shows numerous applications of lubricants for reducing the heat-inducing friction of surface-to-surface contact of the inner surfaces of the collapsed tire. For this purpose, various lubricants have been proposed and/or used which include, for example, (1) solid compositions which will flow at elevated temperatures, (2) a liquid poly(oxyalkylene) glycol and a gelling agent therefor to prevent it from being normally free-flowing and (3) mixtures of various volatile liquids, including water, with lubricating materials such as high molecular weight poly(oxyalkylene) glycol. Although some references teach that some cooling effect is present, the primary thrust is lubrication.
Solid coatings which would only flow under higher temperatures experienced with the running of collapsed tires may be ineffective lubricants by not becoming fluid fast enough to lubricate and save the deflated tire.
Liquid lubricant coatings would appear to be most satisfactory. However, they can be a disadvantage since they would normally have to flow under normal tire operating conditions over a wide temperature range yet still be sufficiently viscous to be effective as a lubricant.
Water has been taught to be useful as a rubber-to-rubber interfacing lubricant but, by itself, is hardly an all-season lubricant, particularly because of its freezing point. Mixtures of water and ethylene glycol, as an antifreeze, have been proposed for this purpose. Mixtures of water and high molecular weight polyethylene glycol have also been proposed with the mixture having a sufficiently high viscosity to be effective as a lubricant and where the water itself could provide some cooling effect with even a possibility of some inflation benefit if it were to vaporize. These systems have not been entirely satisfactory.
For illustrative examples of such prior technical art, reference is made to the following U.S. Pat. Nos.: 4,051,884; 3,739,829; 3,850,217; 4,036,765; British Pat. Nos: 1,443,929 and 1,444,347 and German DAS No. 2706-212.
Indeed, in view of these various problems associated with lubricant application to interior surfaces of tires for the purpose of retarding their breakdown upon going flat, it is still desired to provide an effective means for inhibiting rapid heat build up. A primary difficulty relates to inhibiting, or preventing as long as possible, heat build up, and an accompanying temperature rise, due to internal stresses within the tire carcass itself. It is considered that such internal stresses between the components of the tire are a major source of rapid heat build-up in a collapsed tire being run under load leading to its early failure and that friction due to surface-to-surface contact is a more minor source of rapid heat build-up.
Therefore, it is an object of this invention to provide a tire/wheel assembly which contains a coolant for retarding rapid heat build-up due to at least a partial collapse of the tire while being run under a load.